1. Field Of The Invention
The present invention relates generally to air locks which are designed to allow workers to easily enter and exit a work area, the work area having either contamination which must be contained within the work area or being designated a clean area into which contaminated air must be prevented from entering.
2. Background of the Invention
Requirements for maintaining clean rooms or clean areas have been growing over the years as industry has had a need for maintaining clean manufacturing areas to ensure that parts remain uncontaminated during manufacture. In addition, there has been a great demand to provide means for containing contaminants, such as asbestos, within work areas and thereby prevent particles of the contaminants from escaping into the environment.
Air locks used in industry today usually consist of a relatively large square chamber, having doors on opposing ends for entrance and exit, between a clean and an unclean area. A person enters the chamber, closes the door, and an exhaust fan is turned on to remove the contaminated air that has been trapped within the chamber. The contaminated air is treated before being purged to the environment. One of the major drawbacks in the existing designs of these air locks, is that they are inefficient both in the time that it takes to purge the chamber and the effectiveness of the purging. The time required to open and close separate doors and to purge and treat a relatively large volume of air slows the movement of personnel. Relatively large rooms with four corners are difficult to purge as it is difficult to obtain air movement in the far corners. In addition, the chambers are bulky and difficult to relocate.
A common method for containing contaminants within a work area is to maintain the work area at a lower air pressure than the ambient air so that all air migration will be into the contaminated area and will thus prevent the escape of any contaminated particles entrained in the air. The lower pressure is maintained by removing air from the work area through high efficiency filters which treat the air prior to exhausting to the outside. This requires a measured amount of fresh air to be added to the controlled area as "makeup" air. The amount of makeup air must be regulated to ensure that neither too much nor too little is allowed to enter. This control of makeup air is often provided by allowing air to pass through polyethylene strip curtains that are installed at the entrances to the work area. The curtains remain partially open from the pull of the air passing through the curtains, making it extremely difficult to control the precise amount of air passing through. This results in either too little or too much air flow being permitted into the controlled area. If too much air flow is permitted to enter, the negative pressure is lost and contaminants may be permitted to escape to the environment. Contaminated areas are frequently separated from clean areas by erecting temporary stud walls covered with polyethylene sheeting. If too little air is allowed to enter to control the pressure differential, the polyethylene sheeting may become detached from the temporary walls due to the force of the pressure differential.
More complex structures having showers, baths, air screens, etc. have been employed, and in some cases may be necessary, but for most cases, a simpler and less expensive device will satisfy the control requirements.